Which tool is primarily used for the calculation of flight paths based on inertial sensors?

The Inertial Navigation System (INS) is primarily used for calculating flight paths based on data from inertial sensors. This system tracks the position, orientation, and velocity of an aircraft through the measurement of acceleration and rotation. By continuously integrating these measurements over time, the INS can provide accurate and real-time information about the aircraft's trajectory without relying on external references.

This aspect of the INS makes it particularly effective for navigation in situations where GPS or other external navigation aids may be unreliable or unavailable. It is particularly favored in military and commercial aviation due to its precision and independence from outside signals.

The other options represent different tools or systems but do not primarily focus on the calculation of flight paths based on inertial sensors. For instance, the Flight Data Recorder is primarily used for storing flight data for later analysis, while Required Navigation Performance (RNP) is a specification for aircraft navigation accuracy and not a tool. The Flight Management System (FMS) assists pilots in managing navigation tasks but integrates various data inputs, including GPS, rather than solely relying on inertial sensors. Thus, the INS stands out as the correct choice for this specific function.